Manufacture of cyclohexene



L A m m R 0 G E MANUFACTURE OF CYCLOHEXENE Filed April l5 Patented June 14, 1949 Everett Gorin and Alex G. Oblad, Dallas,

assignots,

Vacuum Oil Company, N. Y., ay corporation of Tex.,

by mesne assignments, to Socony- Incorporated, New York, Texas Application April 15, 1946, Serial No. 662,154

2 Claims. l.

This invention relates to a continuous process for the production of cyclohexene from pentenes. In particular, this invention is concerned with the thermal synthesis of cyclohexene from a mixture of straight chain pentenes containing Z-pentene and l-pentene in such relative proportions that upon pyrolysis approximate stoichiometric quantities of ethylene and 1,3-butadiene, hereinafter referred to as butadiene, suitable for thermal condensation to cyclohexene, are produced. By means of our process cyclohexene and alkyl derivatives of cyclohexene may be synthesized from olenic hydrocarbon fractions consisting substantially of pentenes. The pentene fraction of cracked paran wax or cracked paraiinic naphthas, or the pentene fraction of Fischer- Tropsch naphtha produced from hydrogen and carbon monoxide over iron or cobalt catalyst is particularly suitable feed material to our process.

It is known to condense ethylene and butadiene to produce cyclohexene. Thus, Joshel in U. S. Patent No. 2,349,232 teaches a batch process wherein ethylene is condensed with a 1,3-diene such as Lil-butadiene in stoichiometric proportion corresponding to one mole of butadiene per mole of ethylene. Since it is highly essential to maintain relatively high ratios of ethylene to butadiene in the condensation reaction in order to minimize dimerization of the butadiene and since substantial dilution of the reactants with non-reactive paraihnic hydrocarbons and with other olens reduces the condensation reaction rate and the yield of cyclohexene product, it is highly desirabler to utilize reactants of relatively high purity. The

chief problem, therefore, in the manufacture of cyclohexene by the condensation of ethylene with butadiene is to obtain butadiene and ethylene of high purity without the use of elaborate and extensive fractionating equipment. Expensive low temperature fractionating equipment is usually required to concentrate the ethylene obtained in cracked gas streams. Likewise, very elaborate fractionating equipment heretofore has been used to isolate a C4 fraction containing Ya high percentage of butadiene.

It is the object of this invention to manufacture l cyclohexene from oleiinic hydrocarbons in a continuous process which utilizes a minimum of fractionating equipment. Another object of this invention is to manufacture cyclohexene from straight chain pentenes. Still another object of the invention is to manufacture cyclohexene from a mixture consisting essentially of l-pentene and 2-pentene and containing at least one mole of 2-pentene for each mole of 1-pentene in said mixture. A further object of the invention is to provide a unitary continuous process for the manufacture of cyclohexene by the condensation of relatively pure streams of butadiene and ethylene prepared from straight chain pentenes in a cooperating pyrolytic decomposition step. Other objects of the invention will appear hereinafter.

We have found that mixtures of straight chain pentenes containing 1-pentene and 2-pentene in relative amounts within the range of from about 1 mole of 2-pentene to 1 mole of l-pentene and 9 moles of 2Dentene to 1 mole of 1-pentene can be pyrolyzed at temperatures within the range of from about 725 C. to about 850 C. to decompose of said pentenes and give a product containing atleast 19 mole per cent of butadiene and an approximately equimolar per cent of ethylene. The'yield of propylene on a mole basis is con siderably less than the yield of ethylene and is of the order of about 10 mole per cent. Other components of the pyrolyzed product mixture consist of hydrogen and methane, the sum of the mole per cents of which is usually less than the mole per cent of butadiene or ethylene in the product. The pyrolyzed product contains a relatively small amount of parailinic hydrocarbons other than methane and the C4 cut of the product gas usually contains at least 75% of butadiene.

As indicated hereinabove, the feed to the pyrolysis -step of our process consists of straight chain pentenes, a major portion of which consists of z-pentene. We prefer a pentene stream which is substantially free of branched chain pentenes. Since the pentene cut of most olenic hydrocarbon naphtha streams predominate in i-pentene we usually first subject the pentene cut to a catalytic isomerization step to convert at least a part of the 1-pentene to 2pentene. We prefer to carry out this step in the presence of an alumina gel type catalyst prepared as described hereinafter. The isomerization may be carried out to produce equilibrium proportions of Z-pentene, that is, up to about mole per cent of the straight chain pentenes without producing branched chain pentenes by secondary isomerization. The isomerized product, the Z-pentene content of which amounts to at least 50 mole per cent, preferably from about 60 to 75 per cent of the straight chain pentenes. is passed to a pyrolyzing zone maintained at a temperature of from about 725 C. to about 850 C., preferably from about 760 C. to about 820 C.

The pentene stream is pyrolyzed in the presence of from about 3 volumes to about 15 volumes of a diluent such as steam per volume of pentenes 3 for a periodwithin the range of from about 0.05 second to about 0.5 second, that is.` at a reaction time in the pyrolyzing zone such that at least 40 .per cent and not more than 80 or 90 per cent of the pentenes is reacted .per pass through said zone. The total. pressure in the pyrolysis zone should be within the range of from about atmospheric to about three atmospheres gage. The reaction product is quenched with water and fractionated to obtain relatively pure ethylene and butadiene streams containing substantially equimolar amounts of the two reactants for use in the condensation step o! the process.

The butadiene is added to the ethylene vapor at a pressure of about 150 atmospheres in a condensation reactor or reactor system of any suitable type maintained at a temperature within the range of from about 300 C. to about 375 C., preferably from about 315 C. to 350 C. An internal ratio of ethylene to butadiene of at least 5 to 1 to 30 to 1 or higher is maintained in the condensation reactor.

The total residence time of the ethylene-butadiene mixture in the condensation reaction zone is a function of the temperature and pressure, that is, the residence time should be shorter the higher the temperature and pressure. In general, the residence time employed, expressed in hours, should be within the limits given by the expressions n :ava-T 513-1' 1 5PQX10M4( T and gxloasi( T where P is the total pressure in atmospheres and T is the temperature in degrees Kelvin. Thus, if P=150 atmospheres and T=573 K. the residence time should be between one and four hours. A minimum residence time of about 0.04 hour, that is, 2.4 minutes in the reaction zone and a maximum residence time of about minutes, is suitable when operating at about 300 atmospheres and 375 C. and a maximum residence time of about 8.5 hours is necessary when operating at 300 C. at a pressure of 70 atmospheres and at ratios of ethylene to butadiene within the range of from about 5 to 1 to about 30 to l.

The product is passed to a fractionator for separation of cyclohexene, ethylene, `unreacted components of the C4 fraction and butadiene polymer. The unreacted components of the C4 fraction, consisting mainly of Z-butene, and the butadiene polymer .fraction are recycled to the pyrolysis zone Ifor conversion to ethylene and butadiene. The ethylene is recycled to the condensation reaction zone. For the better understanding of our'invention, reference may be made to the drawing which forms a partof this specii'lpation and represents diagrammatically one form of apparatus suitable for effecting the process of the invention.`

Turning now to a detailed consideration of the drawing the liquid charge is introduced to fractionator I0 by means of pump II inline I2. This charge preferably consists of the straight chain olefinic fraction of a light naphtha obtainable from thermally cracked paraiin wax or from a mixture of synthetic hydrocarbons produced in the Fischer-Tropsch synthesis wherein a cobalt or an iron catalyst is used to convert a mixture of hydrogen and carbon monoxide toV hydrocarbons. Dehydrogenated light naphtha, substantially free of butenes, may also be used as feed material to fractionator l0. The distillation 'range of the oleiinic naphtha should include the pentene fraction and usually should lie within theA limits of from about 20 C. to about 120 C. and the naphtha should consist substantially of straight chain oleiins. The naphtha is fractionated in tower l0 to produce an overhead fraction consisting substantially of straight chain pentenes and a higher boiling olefinic fraction which is withdrawn as bottoms through line I3. Fractionator I0 is operated at pressures from about atmospheric up to three or Yfour atmospheres gage. The straight chain pentene fraction passes overhead through line i4 to coil l5 in furnace I6 where it is heated to a\temperature within the range of from about 200 C. to about 350 C. The hot pentene vapors pass from coil I5 to line l1 which leads to an isomerization zone 20. If the C5 fraction contains an appreciable amount of paraflinic material it is desirable to remove the paramns in an extractive distillation tower (not shown) before passing the C5 olens to the isomerization zone.

Isomerization zone 20 may suitably consist of a series of two or more reactors which are packed with a refractive-type catalyst which is selective for the isomerization of l-pentene to Z-pentene. At least two reactors are manifolded in parallel in order that the castalyst in one of the reactors may be be operated pn stream for the reaction cycle while the catalyst in the other reactor is being regenerated by oxidizing the carbon deposited thereon in said reaction cycle.

The reactors in reaction zone 20 are packed with an activated alumina catalyst. We prefer to use' an alumina gel catalyst prepared from amalgamated aluminum according to the method described by Heard in U. S. Reissue Patent No. 22,196. Catalyst particle size within the range of from about 4 mesh to about 20 mesh may be used as packing in the towers in isomerization zone 20. The catalyst may be deposited in trays or it may be used in a continuous bed. This catalyst is particularly eiective for the isomerization of l-pentene to 2-pentene. Equilibrium conditions for the conversion are easily attained with minimum cracking, minimum polymer formation, and minimum secondary isomerization to branched chain pentenes.

When using the preferred alumina catalyst we prefer to operate the isomerization step of our process at temperatures within the range of from about 250 C. to about 350 C., preferably about 275 C.to 300 C., and at space velocities Within the range of from about 0.5 to 20 volumes ci' pentenes (liquid basis) pervolume of gross catalyst space per hour. As indicated hereinabove, the extent of the isomerization of l-pentene to 2-pentene in isomerization zone 20 is regulated to produce a mixture of l-pentene and 2-pentene such that when the mixture is pyrolyzed approximately equimolar percentages lof recoverable ethylene and butadiene are present in the pyrolyzed product. Hence, the choice of operating conditions within the above ranges is made to accomplish this result. Temperatures much in excess of 325 C. should be avoided, particularly when maintaining low space velocities, since the straight chain pentenes are readily converted to branched chain pentenes, such as trimethylethylene, at higher temperatures. The isomerization reaction is carried out at pressures of from about atmospheric to about three atmospheres gage.

As -indicated above, we prefer that the pentene stream passing to the pyrolysis step of our process contain no branched chain pentenes. branched chain pentenes are present. isoprene is formed and additional fractionation to remove vdrocarbons, and also the isoprene is then made necessary. Hence, if desired, the pentene stream before or after isomeriuation may be treated with an aqueous solution oi sulfuric acid of from about 40 per cent to about 75 per cent acidity to remove branched chain pentenes from the pyrolysis zone feed stream. This may be accomplished in the manner described in our copending application entitled Manufacture of dienes," Serial No. 651,- 015, hled February 28, i946, (now abandoned) by directing the pentene stream in line it or in line di to a sulfuric acid-treatingzone before passing to the isomerization step or to the pyrolysis step.

The isomerized product passes from zone it through lines 2l and t2 to line it which leads to the pyrolyzing coil it in furnace it. In line 23 the pentenes are diluted with from about 3 volunies to about volumes of an inert diiuent. such as superheated steam, introduced to line 2t from line 2d. In coil 2H the mixture oi' steam and pentene vapors is heated to a temperature within the range of from about 725 C. to about 850 C; The vapors pass through coil 24 at a space velocity such that they are subjected to a temperature within the above range for a contact time of from about 0.05 second to about 0.5 second. The term contact time as used in the specication and claims is calculated by dividing that volume of the reactor coil 2t which is maintained within the above temperature range by the total volume oi pentenes and diluent entering the reaction coil per second, measured at standard conditions of temperature and pressure.

We prefer to operate the pyrolysis step of our process at such contact times in the pyrolysis zone that at least 40 per cent and no more than about 3o per cent of in order to minimize the decomposition of Z-pentene to ethylene, propylene, and other non-condensable hyto minimize the condensation of the butadiene product to cyclic hydrocarbons. The pyrolyzed vapors pass from coil 2t to line it and are quenched with water introduced thereto from line di by means of pump 2t in line it which connect with line 2. The pyrolyzed mixture oi hydrocarbon vapor and water vapor passes through line 3d to condenser to and thence by line iii to gas separator t2.

in gas separator t2 condensed steam and any tarry product formed in the pyrolysis` of the pentenes is separated from the gaseous hydrocarloon product of pyrolysis. The liquid condensate is sent to a tar separator (not shown in the drawing) and the water is recycled to line 2l via lines and 2d. At least a part of this water is withdrawn from line di and is passed through line tt to steam generator tt. From generator t5 steam passes via line tt to line 25 to be used as diluent oi' the pentenes undergoing pyrolysis in coil 2t.

The vapor-overhead product from separator di, which comprises pentene decomposition products, undecomposed pentenes, and water vapor, passes overhead through line M. They vapors are raised to a pressure of from about 200 to 250 pounds per square inch i0 and are passed through line #i9 to condenser 50 where additional water vapor is condensed. The mixture of vapors and water passes through line di to separator 52. Water is withdrawn from the bottom of separator 52 through line 53 which joins line 29. The vapors from separator 52 pass overhead through line 5t to drier 55vwhere residairain partially condensed product mixture passes' through line 59 to fractionator 80, which is operated at a pressure of from about 400 to 450 pounds per square inch gage. A part of the hydrocarbon product may condense and Yi'orm a separate layer in separatorA 52. This may be passed to fractionator G0 through a line (not l accumulator t5 comprising propylene,

the pentenes is decomposed per pass through the heating zone by means of compressor i shown) which connects separator 52 with line 59. The product is fractionated in fractionator 60 to produce a bottom draw-oli stream consisting essentially of 1,3-butadiene, 'C4 hydrocarbons other than 1,3-butadiene, unreacted pentenes, and small amounts of other heavierhydrocarbons. and an overhead vapor stream consisting of propylene, C2 hydrocarbons, methane, and hydrogen. The higher boiling product is withdrawn through line 6| and passes to the butadiene recovery system described hereinbelow.

The overhead product from iractionator to passes through line 62, reflux condenser B3, and lineGll to reiiux accumulator 65. Condensate in a small amount of ethane, and a part of the ethylene component of the product stream is withdrawn by means of pump t6 in line 6l, a part of the liquid being returned through line 6d to tower t@ as redux. The remainder of the liquid stream inline 61 is passed through line 69 to fractionato'r 'i0 for the separation of propylene from the C: hydrocarbons and lighter product. Fractionator luis operated at a pressure of from about 450 to 500 pounds per lsquare inch. Vapor overhead from fractionator 'i0 consisting of C2 hydrocarbons, a major proportion of which is ethylene and lighter product, passes through line 'il to condenser 'i2 and thence by line i to reflux accumulator l5. Condensate in accumulator l5 consist ing substantially of ethylene and a` small amount of ethane is withdrawn by means of pump 'it in line Tl, and at least a part of the liquid is passed through line i8 to tower iii as reux. IThe remaining part of the liquid in line 'il is passed through lines 'i9 and 80 to ethylene absorption tower 8i. If desired, at least a part of the ethylene stream in line i9 may besent directly through line 02 to line i0u' through which substantially pure ethylene is passed to the ethylene-butadiene condensation step of the process. The light overhead gaseous streams from accumulators 65 and l5, which contain hydrogen and ethane and a part of the ethylene from the product stream, pass through lines 83 and 8d respectively to line 85, which leads to line 80. A j

Liquid propylene is withdrawn from fractionator 'i0 through line 86. This product may be combined with the ethylene stream in line itu with which line 86 connects. When propylene is combined with the butadiene in the condensation step of our process, 4methylcyclohexene1 is produced as well as cyclohexene. Since we preier to produce relatively pure cyclohexene only, propylene from tower 'l0 is preferably withdrawn from the system through line 01, which connects with line 86. This propylene may be used as feed stock to an alkylation or polymerization process for the synthesis of valuable hydrocarbons.

The stream of light hydrocarbons and hydro gen in line will contain from about. as mms m..

7 -cent to 50 or 55 mole per cent of ethylene, and it of from about to 35 C. with an aqueous solution containing cuprous chloride introduced to tower 8| by means of pump 8,8 in line 89. Contact of the gas with this solution is made at pressures within the range of from about 3 atmospheres to about 30 atmospheres. The use of an aqueous solution of cuprous chloride for absorbing ethylene from a gas stream is described by Gilliland and Seebold in Industrial and Engineering Chemistry, vol. 33, Sept., 1941, pages 1143-1147. The solution recommended by these authors should contain 3 gram moles of ammonium chloride per liter, y approximately 2.5 gram moles of hydrogen chloride, and approximately 2 gram moles of cuprous chloride. Such a solution is particularly adaptable for the removal of ethylene from a pyrolyzed hydrocarbon theA liquid condensate stream since unstable copper acetylides arelnot formed in strong acid solution of the cuprous chloride. As the solution ows downward over the packing in tower 8|, the ethylene is absorbed from the gas and the non-absorbed gases pass overhead through line 90.

The ethylene-enriched solution is withdrawn from tower 8| through line 9| and pressure release valve 92, and passes thence to desorption tower 93. The ethylene may be desorbed from the solution by the reduction of pressure on the solution and/or by the application of heat to the solution by means of steam coil 94 in the bottom of tower 93. Desorbed cuprous chloride solution is recycled from the bottom of tower 93 through line 95 which leads to line 89. If desired, a solution cooler (not shown) may be installed in line 95 in order to maintain the temperature of theV solution within the range of 5 to 35 C. A'relatively pure ethylene stream passes overhead from tower 93 through line 96, which joins line |00 leading to the condensation step of our process. If desired, a part of the relatively pure ethylene stream may be diverted through line 91 by means of blower or compressor 98 for introduction near the bottom of tower 8 i. The introduction of pure ethylene ata point in tower 8l below the point of introduction of the impure ethylene stream serves to strip the solution of any absorbed propylene and substitute therefor absorbed ethylene. Y

Returning now to the description of the recovery of butadiene from the stream of hydrocarbons in line 6|, the mixture passes to'fractionator |0|, which is operated at a pressure of from about 5 atmospheres to about `10. atmospheres gage. The C5 and higher boiling hydrocarbon fraction consisting substantially of undecomposed pentenes, that is, usually at least 80 mole per cent of undecomposed pentenes, is withdrawn from tower |0| through bottom draw-olf line |02. A part of this fraction may bev removed from the process through line |03; however, we prefer to recycle this fraction through line |04 and heater |05 wherein the fraction is vaporized and the vaporized fraction passes through lines lll, 22, and 23 to coil 24 in furnace I3. The vaporized C4 fraction, atleast '75 mole per cent of which is butadiene, passes overhead from tower |0| through line ||0 to condenser I|| and thence through line ||2 to reflux from drum ||3 is by means of pump ||4fin line i5 through line ||6 to be' used as reiiux in tower |01. The remainder of the condensate containing a relatively high per cent of butadiene is passed through line H1 to manifold feed line |20 which 'supplies butadiene t the condensation step of our process. Aesmall amount of aniline or other volatile inhibitor may be added to the butadiene in line in order to inhibit oxidation and poylmerization of the butadiene in the condensation reactors.

The condensation apparatus, wherein ethylene and butadiene are condensed to form cyclohexene, may suitably consistof a multiplicity of high pressure reactors connected in series with the ethylene feed stream and in parallel with the butadiene feed stream. These reactors are represented by chambers |2|, |22, |23, and |24 respectively. Ethylene in line |00 is picked up by compressor in line |26. The compressed gas is passed through heater |21 where it is heated preferably to a temperature within the range of from 315 C. to 350 C. The heated gas passesr through lines |28 and |29to reactor |2|. The ethylene is circulated through the reactor system in order to introduce a high concentration of ethylene therein before introduction of the butadiene. The gas passes from reactor |2| through line |30'to reactor |22, thence to reactor |23, and thence through line |32 to reactor |24.

- stream passes through line |33, valved line |34,

open position. Valve and line |35 to line |26, valve |36 in line |31 being closed. When the reactor system has been heated and pressured, valve |38 in line |34 is closed, and valve |36 in line |31 is placed in the |40 in line |20 is' then opened to inject butadiene to the hot stream of ethylene vapor in line |29 leading to reactor |2|.

- diene to ethylene.

We maintain an ethylene-to-butadiene ratio of at least 5 to 1 in reactors |2I, |22, and |23. The ratio increases as the reaction mixture passes through the series of reactors. The temperature in the reactors is preferably maintained within the range of fromabout 315 C. to about 350 C. Pressure in the reactors may be'from about 70 ,atmospheres to about 300 atmospheres, preferably about 150 atmospheres. The average residence time of the ethylene-butadiene mixture in reactor I2|, when operating at 300 C. and about 150 atmospheres pressure, is within the range o1. from about 30 minutes to about 90 minutes. The reaction mixture passes as a continuous vapor stream to reactor |22 to which additional buta-r diene is added from line |4i, which leads from line |20 and connects with line |30. The.average residence time of the reaction mixture in reactor n |22 which is maintained at approximately the same temperature and pressure as reactor I2|, is within the range of from about 15 minutes to about 60 minutes. ',Ihe reaction mixture passes through line |3| to reactor |23 which is maintained at about the same temperature and pressure as reactors |2| and |22. Additional butadiene may be introduced to reactor |23 through line |42 in order to maintain the ratio of buta- The average residence time of the reaction mixture in reactor |23 is within the range of from about 10 minutes to about 40y minutes.

The reaction mixture passes from reactor` |23 drum H3. Apart ofv passed From reactor |24 the ethylene.

` contain a small amount of anatre 9 through line lll to reactor |24. residual butadiene in the mixed reactantgases is condensed with the ethylene. The residence time in reactor |24 will vary from about 5 to about 30 minutes and the reaction mixture passes through lines E33 and |31 -to partial condenser N3 wherein butylenes, cyclohexene, and butadiene dimer are condensed from the gaseous mix. ture. The mixture of ethylene gas and liquid product passes through line IM' to gas separator itt. Ethylene is recycled from separator Ml through lines M6 and i3! condensate from separator line Ml to fractionator M8. I

Fractionator M8 is operated at a pressure of from about 5 to about 10 atmospheres for the separation of the liquid product from residual ethylene which passes overhead through line E to line lit. Butadiene dimer is withdrawn from iractionator M3 through line M9 which connects `mth recycle line IIN. This butadiene polymer is vaporizecl in heater and the vapor is recycled to coil it through lines |06, 22, and 23. Relatively pure cyclohexene product is withdrawn from fractionator M0 through line 650.

In reactor l2! H5 passes through A Ci stream consisting substantially of 2butene is withdrawn from fractionator |48 through trapout line iti. If desired, this stream which may butadiene may be recycled to coil M via lines tt and itt, heater tdt, and lines ltd, it, and it.

As a speciic example of the operation oi' our invention, 100 moles of straight chain pentenes, a major proportion of which consists of ipen tene, may be isomerized to a mixture containing about 63 moles of 2-pentene and 37 moles of ll-pentene. This mixture is then pyrolyzed at about 800 C. to produce about 24:0 moles oi gaseous product including about 50 moles of unreacted pentenes. Approximately 19 or 20 mole per cent of the 240 moles of product consists oi ethylene and i9 or 20 mole per cent consists of butadiene. These two products can be condensed to produce about moles of cyclohexene from the product of a single pass through'- coil it in furnace it. By recycling the 50 per cent of un- Y converted pentenes approximately d0 moles oi eyclohexene can be obtained from i00 moles oi pentene feed to the process.

To recapitulate. our invention is particularly concerned with improvements in the method ci preparing reactants for the production oi cy elonexene. We utilize a pentene stream contamina" i-pentene and 2pentene in such proportions that when pyroiyzed the product will contain substantially equimolecular yields of ethylene and butadiene. These reactants are present in the pyrolyzed product stre in soient concentration to maire possible their i `ery and use in a relatively pure state in the condensation reaction to produce cyclohex without the exto line |26. Liquid 'l l mol per cent oi said tid penditure of large sums of money in fractionating equipment.

It will be understood that the ow diagram in the art in the light of this that our invention is not restrictive to the details shown. IThus, we may use a smaller number or a greater number o! reaction chambers in the condensation 'step of` our process. 'Onthe other hand, it will be understood that this dow diagram is simplified for the purpose of convenience and that various additional items such as pumping and compressing equipment, heat exchange equipment, control devices, and various other details are not indicated.

We claim:

i. The process for the manufacture of cyclohexene which comprises pyrolyzlng a mixture consisting substantially of 42pentene and from to 5,0 mol percent oi i-pentene in the presence of from about 3 to about 15 volumes'oi steam diluent per volume of pentenes ata temperature within the range of from 725 C. to 850 C. for a contact time of from about 0.05 to 0.5 second to decompose from to 90 mol percent of said pentenes and'to produce substantially equal molar quantities of ethylene and 1,3-butadiene, separating and recovering the ethylene and i,3butadiene from the pyrolyzed mixture, and condensing the 1,3-butadiene and ethylene to produce cyclohexene.

2. The process for the manufacture of cyclohexenewhich comprises pyrolyzing a mixture of pentenes substantially free from branched chain pentenes and consisting substantially of 2pen- 4tene and from 10 to 50 mol percent of 1-pentene in the presence of from about 3 to about 15 volumes of steam diluent per volume of pentenes a temperature within the range of from '725 C. to850 C. for a contact time of from about 0.05 to 0.5 second to decompose from 40 to 90 pentenes and to produce substantially equal molar quantities of ethylene and 1,3-butadiene, separating and recovering the ethylene and Lid-butadiene from the pyrolyzed mixture, and condensing the 1,3-butadiene and ethylene to produce cyclohexene.

n e nonne.

n. on.

litlElFlENCEd The toll references are ot record in Frey 12, 1946 Certiicate of Correction Patent No. 2,473,472 June 14, 1949 EVERETT GoRIN ET AL. s i It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

In the grantline 4, and in the headiii/g to the printed specification, line/6, State (if incorporation, for Texas read New ork; 4column 6, line 43, for line 7 read 'ine 73;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 24th day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommz'asoner of Patenti. 

